Capacity of Listeria monocytogenes Strains from the 2011 Cantaloupe Outbreak To Adhere, Survive, and Grow on Cantaloupe

Abstract

The 2011 listeriosis outbreak attributed to whole cantaloupe involved several genetically distinct strains of serotypes 1/2a and 1/2b that had not been previously reported in invasive listeriosis outbreaks. Here we investigated the potential of strains from the 2011 cantaloupe outbreak to adhere, survive, and grow on cantaloupe rind and flesh and in juice extracted from cantaloupe at different temperatures (4, 8, and 25°C). All strains were able to adhere and grow, with ∼10-fold increases after 7 days at 4 or 8°C and after 24 h at 25°C, with a propensity for more growth on rind than on flesh or in extract. No significant differences in growth potential were noted among the different strains or between them and unrelated strains from other listeriosis outbreaks involving celery, deli meats, or hot dogs. Similarly to the cantaloupe outbreak strains, these other strains exhibited greater propensity for growth on rind than on flesh or in extract. Rinsing of cantaloupe fragments in sterile water resulted in temporary reductions of the populations by 50- to 100-fold, suggesting the potential of such washing to reduce risk if the produce is promptly consumed. The absence of marked differences in adherence or growth between the cantaloupe outbreak strains and strains from other outbreaks highlights the need to further characterize the 2011 cantaloupe outbreak strains and elucidate potential biological attributes that contributed to their implication in the outbreak.

RNA Helicase Mediates Competitive Fitness of Listeria monocytogenes on the Surface of Cantaloupe

“…While previous Horticulturae 2018, 4 studies have investigated the relation between flagellar motility and biofilm formation [2,6], limited information is currently available on the potential role of motility in colonization of fresh produce. When stored at 4 and 20 • C for 15 days, L. monocytogenes was able to survive on whole cantaloupe, but exhibited a 1 to 2 log 10 CFU/cm 2 decline in one study [7], while it was able to grow on the rind of cantaloupe in another investigation [8]. Previous work implicated both the formation of flagella and motility in the ability of L. monocytogenes to adhere to produce [9,10].…”

“…Bacterial strains that were used in this study are listed in Table 1. Mutant libraries were constructed as described previously [17,18] in the serotype 1/2b strain 2011L-2858 (hereafter designated as strain 2858), isolated from cantaloupe that were implicated in the 2011 cantaloupe outbreak [1,8].…”

“…At retail, cantaloupes were displayed at room temperature and they were kept at room temperature during transportation to the laboratory where they were used within 2 h of purchase. Rind fragments (5 × 5 × 1 cm) were prepared as described [8] and placed rind side up in groups of four into labeled, sterile plastic petri dishes (100-mm diameter, Fisher Scientific, Pittsburgh, PA, USA). Cantaloupes were subject to selective enrichments to rule out native contaminating L. monocytogenes, as described in Azizoglu et al (2014) [19].…”

“…Cantaloupes were subject to selective enrichments to rule out native contaminating L. monocytogenes, as described in Azizoglu et al (2014) [19]. Each fragment was spot-inoculated as described [8] in 10 evenly separated droplets of 10 µL each (total inoculum 100 µL, corresponding to approx. 10 5 CFU/fragment); two fragments were inoculated for each time point, and several fragments similarly spotted with sterile water as controls.…”

“…Previous work implicated both the formation of flagella and motility in the ability of L. monocytogenes to adhere to produce [9,10]. The objective of this study was to characterize two mariner-based non-motile mutants of L. monocytogenes 2011L-2858, a serotype 1/2b strain from the 2011 cantaloupe outbreak [1,8], regarding their colonization potential and fitness on cantaloupe rind.…”